Abstract: The Feynman’s path integral theory is introduced into quantum mechanics

teaching，and used to analyze photon interference. The correlation functions of nondegenerate

two - photon and three-photon interference are derived. The results of interference are

simulated. The simulate results show that multi-photon interference of nondegenerate

　　photons results from the superposition of multi-photon bunching and quantum beating effect.

Key words: multi-photon interference, path-integral theory, quantum beating